package util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

/**
 * Created by zzz on 2016/11/23.
 */
public class CheckUtil {

    private static final String token = "xupt";

    /**
     * 1）将token、timestamp、nonce三个参数进行字典序排序

     * 2）将三个参数字符串拼接成一个字符串进行sha1加密

     * 3）开发者获得加密后的字符串可与signature对比，标识该请求来源于微信
     * @param signature
     * @param timestamp
     * @param nonce
     * @return
     */
    public static boolean checkSignature(String signature, String timestamp, String nonce) {
        String[] arr = new String[]{token, timestamp, nonce};

        //排序
        Arrays.sort(arr);
        //生成字符串
        StringBuffer content = new StringBuffer();
        for (int i = 0; i < arr.length; i++) {
            content.append(arr[i]);
        }

        //sha1 加密
        String temp = getSha1(content.toString());

        return temp.equals(signature);
    }

    /**
     * sha1 
     * @param str
     * @return
     */
    public static String getSha1(String str){
        if (str == null || str.length() == 0) {
            return null;
        }
        char hexDigits[] = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
        try {
            MessageDigest mdTemp = MessageDigest.getInstance("SHA1");
            mdTemp.update(str.getBytes("UTF-8"));
            byte [] md = mdTemp.digest();
            int j = md.length;
            char buf[] = new char[j * 2];
            int k = 0;
            for (int i = 0; i < j; i++) {
                byte byte0 = md[i];
                buf[k++] = hexDigits[byte0 >>> 4 & 0xf];
                buf[k++] = hexDigits[byte0 & 0xf];
            }
            return new String (buf);
        } catch (Exception e) {
            return null;
        }


    }



}
